A pump of the above kind is also known as a screw pump and is disclosed in German Patent No. 1,903,069. A rotor having a multiple spiral slot is attached to a shaft having a smooth outer surface in the manner of a roller bearing. The rotor rotates in a stator configured as an outer ring and the stator includes a suction connection for the pressure connection. The stator carries sealing plates at its axial ends which seal the pump with respect to the ambient. In order to make the operation of the known pump reliable, the pump must be submerged as deeply as possible in the liquid to be pumped.
If the pump lies only partially in the liquid to be pumped or outside of the latter, then it must be assured that no air can penetrate into the system to assure reliable operation. However, it has been shown in practice that play occurs between the stator and the rotor because of wear and this leads to a short circuit between mutually adjacent turns of the slot and also causes air to penetrate into the pump system. A short circuit between mutually adjacent turns as well as air in the system leads to a reduction of pump capacity and can also lead to a failure of the pump. Also, assembly errors such as a tilting during assembly can lead to a rapid pump failure.